Cushion tire and method of making the same



Nov. 9, 1926. 1,606,503

R. S. BURDETTE CUSHON TIRE AND METHOD OF MAKING THE SAME Filed June 19 1925 i INVEN-roR 'llcbard .IBurdeHe,

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ATTORN EY Patented Nov. 9,1926.

UNITED STATES IRI CHARD S. BURDETTE, OF AKRON, OHIO, ASSIGNOR TO THE GOODYEAR TIRE & RUB- PATENT OFFICE.

BER COMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO.v

CUSHION TIRE AND METHOD OF MAKING/THE SAME.

Application led .Tune 19, 192.5. Serial No. 38,380.

` My invention relates to cushion tires and it has for its primary object the provision of a process of manufacturin such tires which will result in securing esirable'operating characteristics.

vHeretofore it has been customary to make solid or cushion tires by extruding rubber stock in a tube mill through a die, to form sticks of tread material. `It has been proposedto form the die of4 such shape that the resulting stick will have a crosssec' tional area corresponding substantially to that desired for the finished. tire.

To groovethe stick, in order to form a cushion tire, it has been proposed to place a V-shaped `cutting tool in the aperture of the die. y

Sticks of. tread material for solid cushion tires made in this manner are cut-tothe required length and cemented to a metal tire rim or base band, through the medium of a hard rubber strip. Soft rubber, fromV which the tread is made, does not adhere readily to metal.` Hard rubber is inserted between the metal and the tread and adheres to both when the tire is vulcanized.

There are several phenomena occurring in this process which materially affect the finished product. They may be discussed and the present invention explainedv by reference to the accompanying drawings, wherein:

Fig. 1` is a cross-section of a tread stick extruded inthe improved process;

Fig. 2 is a cross-section of a tread stick for a solid tire formed under the Vold process;

Fig. 3 is a cross-section of a tread stick for a cushion tire formed under the old process;

Fig. is a cross-section of a tread stick for a cushion tire formed under the new process;

Fig. 5 is a fragmentary view taken on the line-A-A vof Fig. l; and

Fig. 6 is a perspective View of a cutting tool employed in the new process.

One phenomenon which is observed in eX- truding sticks of plastic material is that of distortion. When rubber'or other plastic material is extruded through a die, it must pass throughv an orifice of restricted diameter. After leavingv the orific, it may be said that the kinetic energy, created in the material by passage through the restricted orifice is transformed into potential energy, when the stick emerges into a zone of greater diameter. The resulting transformation of energy causes plastic material to expand in substantially a radial direction. Under certain operating conditions, it has been found that an extruded rubber stick will expand practically 100 percent, that is, the crosssectional area of the stick after equilibrium is Vobtained is practically twice the cross-sectional area of the orifice. Maximum distorton occurs through the center of the v stick. I The expansion is not uniform, vand as a result, the stick lwhich has expanded Vwillnot have a cross-sectional area similar.

to that of the'orifice.

It has. been recognized that economy in manufacturing operations could be obtained by' extruding tread material in the form of a double stick, and subsequently` splitting the stick toform two treads. ever,because of distortion, ithas not been possiblev heretofore to develop a method which would yield asatisfactory stick. Recently a satisfactory method has been developed by which a double stick may be extruded and subsequently cut to form two tread sticks which are of thevproperv shape and size` 'This method does` notpform a part of the present linvention and `need not be referred to in detail. Itis discussed in an vapplication field by Jorgen IfII-Iaase, dated June 19,v waas. N. 38,280.7

A secondphenomenon isthat of grain` effect. Plastic material extrudedtthrough a die hasVaQdeinite grain. As shown in the drawings, the grain is yconcentric to the center-of' the stick. As shown in Fig.l 5, the grainis conical.v The grain effect in extruded rubber is somewhat ,analogous to that in a tree. vlteferring to the drawings, itwill be/seen that in Fig. l. the grain f i is shown by the lines 10 concentric about the centralaxis of the stick. FigZ is a section of asingle` stick which-,has been eX- trucled from a die. Here again"` the rain is exhibitedglfiy'1a series. of concentric 'circles ,around the center of 4the stick.' Fig. 3 shows a section"Sota-.cushion tire which has been extruded through a die having a V-shaped cutting'tool. It Awill be noted here that the grain isgzdistorted. The grain lines lare continuous,v Aform closedv curves, v.and bend aroundvthefp'ortion out from the tire by the V-'shaped cutting tool. It is to*l be parl' ticularly noted in Figs.. 2 and 3 that the grain adjacent that portion of the tire which lies 4next to the hard rubber base band, as indicated at 11, lies either at `an angleor parallel to this surface. NVhen treads hav1ng a grain, such. as

' in Fig. 4, the union between the tread and tread, only a very slight effect Will be ob` rubber composition is warm from tubing,

the hard rubber band is much stronger. This is because the grain is substantially Vnormal to the surface of the band.

*Ithas beenk found that a better union is obtained when the grain is substantially normal to the rim or base band.

The grain effect of the sections shown in Figs. 1 and4 along the base 11 of the tread, is indicated in Fig. 5. Near the outer edges of the tire, the grain lines are substantially parallel to the side walls of the tire. The angularity ofthe grain lines increases toward the center of the tread. In the treads which have a grain according to Figs. 2 and 3, the back 1 1 of the tread does not show eX- actly the same structure. In Figs. 2 and 3, for example, where the contours 10 are substantially parallel to the back 1'1 of the served.

There is one other extruded stock. When unvulcanized soft it may be cut readily. When cold, considerable effort is required to cut a groove through it. Advantage has been taken of the condition of the rubber when wa'rm from tubing in the cutting process, disclosed in the copending application previously indicated. It is. to be understood, of course.

that the .terms warm, hot7 and cold are used in a relative sense. The stick as it( emerges from the extruding'machine is'at a temperature of approximately 180 F. Between this temperature and about 100o F. it may be termed Warm. Below that temperature, ditliculty is experienced in the cutting operation, and it may be said to be cold. These temperatures are merely indicative, they vary with operating conditions and with the nature of stock employed. The plasticity of the material while Warm may be used to advantage in the new method of forming a tread having a section such as shown in Fig. 4.

To form this section, stock is extruded, in the form of a double stick having a crosssectional area, after expansion, asA shown in Fig. 1. The strip is then cut along the line grained as shown by the i `metal knife 6 is -secured to the handle phenomenon occurring of the stick, and

A-A, according to the methodset'. forth in the cop'einding` application. While still warm, a cutting tool, such as shown in Fig. 6, is pulled-throughthe-material to form the central groove l2, shown inFig. 4. 'The prises a handle 5 having an enlarged head..

A metal member 6 havinga cutting edge 7 is bent to a shape substantially the same as that desired for the central groove 12. The 5 by suitable means, such as screws 8.

If the stock is cut after it becomes cold,

' a much stronger cutting tool would berequired. While the structure shown in Fig. 4 can be obtained by cutting after the stock isl cold, it is more desirable to cut while the stockis Warm. I

'From the foregoing description it will be seen that a method has been developed for obtaining tire treads having greatly improved characteristics.- As comparedwith tire .treads made by the older methods the new treads have longer-life andform a better union. i'

While this invention has been described as having particular utility inthe manufacture of solid and cushion tires, it is to be understood that it is not limited thereto. The process is applicable to extrusion operations of materials designed for various uses. The invention should be limited only by the scope of the appended claims.

at Iclaim is:

1. A method of making cushion tires which comprises the steps of extruding a stick of plastic material, splitting the stickV longitudinally and cutting a groove in the stick While it is at a relatively high temperature.

.2. A method of making cushion tire treads which comprises the steps of extruding a stick of rubber which has a cross-sectional area of substantially twice the cross-sectional area of the tread, splitting the stick along a longitudinal a'Xis and across the grain grooving out a central portion of the stick while the stick is .still hot.

3. A cushion tirecomprising` a rim portion and a rubber tread portion formed with a cavity extending circumferentially thereof, the grain lines tially normal to the rim at the rim, and ex- 4tending in substantially regular curves conlRICHARD s.` BURDETTE.

of the tread being substan- 

